I suppose we could print out the parameters that break the classfier but with fold number it could be more tricky because `fit_grid_point()` doesn't know the index of the fold that it is fitting. We could add an extra parameter to let it know that but I'm not sure if the benefit is worth the extra complexity.

Switching from `str(e)` to `repr(e)` seems like a good idea.

Same for providing a switch to raise errors, although again this means an extra parameter for `fit_grid_point()`